Conventionally, an electrographic image forming apparatus, such as a photocopy machine, a facsimile device and a printer, includes an image forming unit for forming an image. The image forming apparatus is configured with a photosensitive drum, a charging part, a development part, a cleaning part, and a toner cartridge, and the like. The charging part, the development part, the cleaning part, and the toner cartridge are disposed around the photosensitive drum. The image forming apparatus forms a toner image on the photosensitive drum. Toner to be supplied on the photosensitive drum is supplied by the toner cartridge that contains toner as a developer installed to an image forming unit main body. The photosensitive drum configuring the image forming unit has a life as a consumable item and needs to be replaced at the end of the life. The toner cartridge to be installed also needs to be replaced when the contained toner runs out. Accordingly, the image forming unit is removably installed to the image forming apparatus main body. Furthermore, the toner cartridge is removably installed to the image forming unit main body. In order to inform a user of a timing for replacing the parts to be replaced, the life of the image forming unit main body and a remaining toner amount are controlled by a controller of the image forming apparatus (see JP Laid-Open Patent Application No. 2006-267528 (page 7, FIG. 4)).
In the conventional art, it is difficult to determine a replacement time of a consumable item when the replaceable consumable item is removed from an apparatus before coming to its life and is installed and used in another apparatus.